As many know (or may not know) all of the terrain and building data for WOW is actually kept client-side. As such if one spent the time to read it and put it all together, they could create a navigation mesh for the entire WOW world from that data. I've started just such a project and gotten pretty far.
I've been blogging step by step what I've done over at MPQNav Public Blog | WOW Navigation from MPQ Files and I thought some people might enjoy reading it. Source code is available after each step at the end of each post.
Hopefully this isn't against any rules (I double-checked and this seemed like the best place to put this) and it is a work in progress but pretty far along.
Enjoy!